The search for a missing Argentine submarine and its 44-member crew has been helped by calmer seas, but there were no new clues about its location and worries multiplied because the vessel may be running out of air.

While the ARA San Juan carried enough food, oxygen, and fuel for the crew to survive about 90 days on the sea's surface, it had only enough oxygen to last seven days if submerged.

The San Juan was last heard from last Wednesday as it journeyed from the extreme southern port of Ushuaia to the coastal city of Mar del Plata.

Submarine crews are trained to evade detection. But that very skill may ultimately cost the lives of the 44 crew on the Argentinian submarine San Juan.

More than a dozen international vessels and aircraft have joined in a maritime search that has become a race against the clock.

An Argentine navy official previously said the submarine reported a battery failure last Wednesday and was returning to the Mar del Plata naval base when it went missing.

Hopes were buoyed after brief satellite calls were received and when sounds were detected deep in the South Atlantic, however experts later determined that neither was from the missing sub.

Locals hold vigil near naval base

The sub was originally scheduled to arrive on Monday at Mar del Plata, about 400 kilometers southeast of Buenos Aires.

Relatives of the crew have gathered at the base to receive psychological counselling and wait for news about their loved ones.